1. Field of the Invention
Present invention relates to network intermediate devices for interconnecting terminals in a network across communication links; and more particularly to techniques used to resolve modes of operation for the links.
2. Description of Related Art
Communication networks consist of terminals that are interconnected by links to network intermediate devices such as repeaters, switches, bridges and the like. The intermediate devices are used to interconnect the terminals to establish paths of communication among the terminals.
As network technologies have developed, a wide variety of techniques have evolved for operating links between terminals and intermediate devices. For example, the ethernet network standard according to the IEEE Standard 802.3, published by the Institute of Electrical and Electronic Engineers, supports a variety of local area network (LAN) technologies. These technologies include the 10 BASE-T standard which specifies a 10 megabit per second carrier sense multiple access with collision detection (CSMA/CD) LAN over two pairs of twisted pair telephone wire, the 10 BASE-F standard which specifies a 10 megabit per second CSMA/CD LAN over fiber optic cable; the 100 BASE-TX standard specifies a 100 megabit per second CSMA/CD LAN over two pairs of category five UTP or shielded twisted pair wire, and a number of other current and emerging technologies. Typically data terminals in a network are designed to support a specific LAN technology. However, network intermediate devices which are designed to interconnect a wide variety of terminals, need a technique for resolving the particular technology used across a link coupled to a particular port of the device.
To meet this need for resolving the LAN technology of a particular link the IEEE standards commissions have developed an auto-negotiation function which specifies physical layer signaling for 10 megabit per second and 100 megabit per second LAN technologies which utilize twisted pair wiring. These technologies include 10 BASE-T, 10 BASE-T full duplex, 100 BASE-TX, 100 BASE-TX full duplex, and 100 BASE-T4. The specified auto-negotiation function is designed to support other technologies and new LAN technologies as they evolve. The auto-negotiation function according to the standard allows a device to advertise enhanced modes of operation that it possesses to a device at the remote end of a link, and to detect corresponding enhanced modes of operation that the other device may be advertising. The auto-negotiation function automatically configures both devices to take maximum advantage of their abilities. The auto-negotiation function is performed at the physical layer relying on link integrity test pulse sequences (including normal link pulses NLPs and fast link pulses FLPs), so that no packet or upper layer protocol overhead is added to network devices for the purposes of this function.
The auto-negotiation function is specified in clause 28 of IEEE Standard 802.3u-1995, Institute of Electrical and Electronic Engineers, Inc., pages 235-280, and associated annexes. Clause 28 is incorporated by reference as if fully set forth herein.
The auto-negotiation function is designed for implementation in the physical layer of each port on the network intermediate devices which utilize the standard. See Clause 28, supra, figure 28-2 "Location of Auto-Negotiation Function within the ISO Reference Model" on page 237. Thus, a twelve port repeater or other intermediate device, will have twelve instantiations of the auto-negotiation state machine. The auto-negotiation state machine is quite complicated, encompassing thousands of logic gates. Thus, the auto-negotiation function significantly increases the cost of network intermediate devices.
Accordingly, it is desirable to provide an auto-negotiation function for network intermediate systems, with a more efficient architecture, so that expensive space on integrated circuits implementing the ports can be saved.